Comparison between the time-averaged projected VSFs of our hydrodynamical (red lines) and MHD (gray line) runs. In the hydrodynamical run, the gas is nearly entirely contained in a disk of radius r_disk ∼ 5 − 10 kpc for times t ≤ 2.7 Gyr. We thus distinguish this specific phase (solid line) from the remaining part of the run (dashed line) where no disk is visible (i.e., for t ≥ 2.7 Gyr).